Seismic data representing a plurality of seismic channels is conventionally digitized and stored on magnetic tape for further data processing. In one such data processing operation, the information stored on the magnetic tape is used to modulate a cathode-ray tube so as to display the information on the face of the cathode-ray tube. Such display can then be photographically reproduced by means of a conventional drum plotter. The photographic reproduction obtained is a series of traces, one such trace for each seismic channel, recorded in a parallel relationship. In such data processing operations, the digitized seismic data stored on magnetic tape is converted to seismic analog signals. These analog signals are then multiplexed so as to provide intensity-modulation pulses for application to the electron beam of a cathode-ray tube as it sweeps across the face of the display. One intensity-modulation pulse is provided during each sweep of the electron beam for each of the seismic channels. Rotation of the drum plotter past the face of the cathode-ray tube results in each sweep of the electron beam being recorded on the drum plotter in a position displaced from the previous sweep, resulting therefrom in a series of seismic trace recordings on the photographic material surrounding the drum plotter. Timing lines are produced on the photographic material at fixed time intervals along the length of the seismic trace recordings.
Timing numbers can be photographically produced on the seismic trace to identify the timing lines in accordance with the teaching of U.S. Pat. No. 3,714,663 to Clarence G. Smith. Selected seismic traces can be marked with lines through the center of the traces for the entire length so that they are readily distinguishable from other seismic traces in accordance with the teaching of U.S. Pat. No. 3,704,450 to Clarence G. Smith. Seismic traces may be annotated with alpha-numeric characters to identify such things as section type, area, shotpoint, etc., in accordance with the teaching of U.S. Pat. No. 3,886,526 to Clarence G. Smith.